Light guide plate with high-density diffusing dots

ABSTRACT

An exemplary light guide plate includes a light input surface, a bottom surface, a light output surface opposite to the bottom surface, and a plurality of dots. The dots are arranged on the bottom surface in series of adjacent columns parallel to the light input surface. A distance between two dot centers of two adjacent dots and sizes of the dots in a same dot column are uniform. Each dot column defines a column axis that passes through dot centers of each of the dots. A distance between two adjacent column axes increases with increasing distance from the first light input surface. A backlight module using the light guide plate is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to light guide plates and backlightmodules typically used in liquid crystal displays, and particularly to alight guide plate having high-density diffusing dots.

2. Discussion of the Related Art

Backlight modules are used in liquid crystal display devices forconverting linear light sources (such as cold cathode ray tubes) orpoint light sources (such as light emitting diodes) into surface lightsources having high uniformity and brightness.

A typical backlight module includes a light source, a light guide plate,a reflection plate, a diffusion plate, and a prism sheet. The lightsource can be located beside an end of the light guide plate or besidetwo opposite ends of the light guide plate. The light source is used toemit incident light rays into the light guide plate. The light guideplate is used to guide incident light rays to exit an emission surfaceefficiently. The reflection plate is located below a bottom surface ofthe light guide plate, and is used to reflect some of the incident lightrays that escape from the bottom surface back into the light guideplate. This reflection enhances the utilization ratio of the incidentlight rays. The diffusion plate and the prism sheet are located on theemission surface of the light guide plate in that order, and are used toimprove uniformity of the emitted light rays.

FIG. 6 shows one example of the above-described kind of backlightmodule. The backlight module 10 includes a light guide plate 11, a lightsource 12, a side reflection sheet 14, a light diffusion layer 16, abottom reflection sheet 15, and a curved reflection plate 17. The lightguide plate 11 includes a light input surface 112, a light outputsurface 114 adjoining the light input surface 112, and a bottom surface116 opposite to the light output surface 114. The light source 12 ispositioned adjacent to the light input surface 112. The side reflectionsheet 14 is provided on a side surface (not labeled) of the light guideplate 11 that is opposite to the light input surface 112. The lightdiffusion layer 16 is disposed on the light output surface 114, and thebottom reflection sheet 15 is disposed on the bottom surface 116. Thecurved reflection plate 17 is provided to substantially enclose thelight source 12 so as to efficiently utilize light rays emitted by thelight source 12.

Furthermore, a plurality of dots 118 configured for lightdiffusion/transmission is provided on the bottom surface 116 of thelight guide plate 11. The dots 118 are formed by means of, for example,gravure printing, offset printing, screen printing and/or transferprinting. The dots 118 can have any of various predetermined shapes,such as round, square, or polygonal. The dots 118 are used to break upwhat would otherwise be total reflection of light rays incident at thebottom surface 116. This light diffusion ensures that the light raysexit an entire expanse of the light output surface 114 of the lightguide plate 11 uniformly.

Referring to FIG. 7, a distribution of the dots 118 on the bottomsurface 116 of the light guide plate 11 is shown. The dots 118 arearranged on the bottom surface 116 in a matrix, which includes a seriesof adjacent columns of dots 118 parallel to the light input surface 112.In a same column, a distance between the centers of two adjacent dots118 is uniform. Each column defines a column axis that passes throughthe centers of the dots 118. A distance between the column axes of twoadjacent columns is uniform. For example, referring to FIG. 8, adistance Y_(pitch) between two adjacent column axes X₁ and X₂ isconstant. Sizes of the dots 118 gradually increase with an increase indistance from the light input surface 112 along a first direction. Thefirst direction is perpendicular to the light input surface 112 andparallel to the light output surface 114.

The dots 118 can, to a certain extent, enhance the uniformity of thelight rays emitted from the light guide plate 11. Sizes of the dots 118near the light input surface 112 are relatively small, thus a clearancebetween adjacent columns near the light input surface 112 is relativelylarge. That is, the sizes of the dots 118 are relatively small, tocompensate for the close proximity of the dots 118 to the light inputsurface 112. However, this means relatively large areas of the bottomsurface 116 corresponding to the clearances are not used for lightdiffusion. In this respect, the dots 118 near the light input surface112 do not provide efficient dispersal of light rays incident at thatpart of the bottom surface 116. Thus, it is difficult for the lightguide plate 11 to achieve a high level of uniformity of light raysemitted from the light output surface 114. Furthermore, clearancesbetween adjacent rows of dots are substantially straight, and this tendsto produce bright lines in the output light. For these reasons, thelight guide plate 11 cannot necessarily provide the backlight module 10with optimal quality of output light.

What is needed, therefore, is a light guide plate and backlight moduleusing the light guide plate that overcome the above mentioneddisadvantage.

SUMMARY

A light guide plate according to a preferred embodiment includes a lightinput surface, a bottom surface, a light output surface, and a pluralityof dots. The bottom surface is adjacent the light input surface. Thelight output surface is opposite to the bottom surface. The dots arearranged at the bottom surface in a series of adjacent columns parallelto the light input surface. Sizes of the dots in a same columnprogressively decrease with increasing distance from a middle of thecolumn to each of two opposite ends of the column. Sizes of the dotsincrease with increasing distance of the columns from the light inputsurface. Each column defines a column axis that passes through centersof the dots in that column. A distance between two adjacent column axesincreases with increasing distance from the light input surface.

In another aspect, a backlight module according to a preferredembodiment includes a light guide plate and a light source. The samelight guide plate as described in the previous paragraph is employed inthis embodiment. The light source is disposed adjacent to the lightinput surface of the light guide plate.

Other advantages and novel features will become more apparent from thefollowing detailed description of various embodiments, when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The components in the drawings are not necessarily drawn to scale, theemphasis instead being placed upon clearly illustrating the principlesof the present light guide plate and backlight module. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views, and all the views are schematic.

FIG. 1 is a side view of a backlight module according to a firstpreferred embodiment of the present invention, the backlight moduleincluding a light source and a light guide plate.

FIG. 2 is a plan view of a bottom surface of the light guide plate ofFIG. 1.

FIG. 3 is a plan view of a bottom surface of a light guide plateaccording to a second preferred embodiment of the present invention.

FIG. 4 is a plan view of a bottom surface of a light guide plateaccording to a third preferred embodiment of the present invention.

FIG. 5 is a plan view of a bottom surface of a light guide plateaccording to a fourth preferred embodiment of the present invention.

FIG. 6 is a side view of a conventional backlight module, the backlightmodule including a light guide plate and a light source.

FIG. 7 is a plan view of a bottom surface of the light guide plate ofFIG. 6.

FIG. 8 is an enlarged view of a circled portion VIII in FIG. 7.

FIG. 9 is an abbreviated, plan view of a bottom surface of an opticalplate in accordance with a fifth embodiment of the present invention.

FIG. 10 is an abbreviated, plan view of a bottom surface of an opticalplate in accordance with a sixth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe preferredembodiments of the present light guide plate and backlight module indetail.

Referring to FIG. 1, a backlight module 20 in accordance with a firstpreferred embodiment is shown. The backlight module 20 includes a lightguide plate 21 and a light source 22. The light guide plate 21 is arectangular sheet, or alternatively may be generally cuneiform. Thelight guide plate 21 includes a light input surface 212, a light outputsurface 214 adjoining the light input surface 212, a bottom surface 216opposite to the light output surface 214, and an arrangement of dots 218formed on the bottom surface 216. The light source 22 is positionedadjacent to the light input surface 212. A material of the light guideplate 21 is preferably selected from the group consisting of polymethylmethacrylate (PMMA), polycarbonate (PC), and other suitable transparentresin materials. In this embodiment, the light guide plate 21 is made ofPMMA, and the light source 22 is a cold cathode fluorescent lamp.

Referring to FIG. 2, an arrangement of the dots 218 on the bottomsurface 216 of the light guide plate 21 is shown. The dots 118 are usedto diffuse light incident thereon. The dots 218 are arranged in a seriesof adjacent columns, all of which are parallel to the light inputsurface 212. Each column contains a line of adjacent dots 218. The dots218 are square when viewed from directly below. The dots 218 have a samesize, and are closely adjacent each other in a same column. Each columndefines a column axis Y_(n) (Y_(n+1), Y_(n+2) . . . and so on), whichpasses through centers of the dots 218 in that column. A distancebetween centers of two adjacent dots 218 in a same column is constant.Furthermore, the distance Y_(pitch) _(—) _(n) (Y_(pitch) _(—) _((n+1)),. . . and so on) between two adjacent column axes progressivelyincreases with increasing distance from a leftmost column nearest thelight input surface 212 to a rightmost column furthest from the lightinput surface 212. The size of the dots 218 in each column progressivelyincreases with increasing distance of the columns from the leftmostcolumn nearest the light input surface 212.

It should be noted that the sizes of at least some of the dots 218 ineach column can be configured to be different from each other, accordingto a position and/or a light distribution characteristic of the lightsource 22. In one example, referring to FIG. 10 the sizes of the dots718 in a same column progressively increase with increasing distancefrom a middle of the column to each of two opposite ends of the column.In another example, referring to FIG. 9 the sizes of the dots 618 in asame column progressively decrease with increasing distance from amiddle of the column to each of two opposite ends of the column.

An area of the dots 218 when viewed from directly below is preferably inthe range from about 1×10⁻⁷ square millimeters to about 1×10⁻⁴ squaremillimeters. The array of the dots 218 are manufactured by printing orchemical etching with a pattern mask. A material of the dots 218 can beselected from a group consisting of printing ink or a suitable modifiedprinting ink. The modified printing ink is formed by uniformlydispersing a plurality of scattering particles into a printing inkmatrix material. Alternatively, the dots 218 can be configured to bemicro-scattering structures etched on the bottom surface 216.

In summary, the distance Y_(pitch) between adjacent column axes Y_(n) isconfigured vary according to varying distances of the columns from thelight input surface 212, and the dots 218 in a same column are arrangedclosely together. Therefore, even though the dots 218 in columns nearthe light input surface 212 are relatively small, a clearance betweenadjacent columns near the light input surface 212 can be configured tobe very small. Thus a great majority of the bottom surface 216 is usedfor light diffusion, and the dots 218 near the light input surface 212provide efficient dispersal of light rays incident at that part of thebottom surface 216. Further, each dot 218 in each column is offsetrelative to the adjacent dots 218 in each of the adjacent columns. Thismeans, unlike in the above-described conventional light guide plate 11,there are no straight clearances between adjacent rows of dots; andtherefore there are no corresponding bright lines in the output light.For these reasons, the light guide plate 21 can provide optimal qualityof output light.

Referring to FIG. 3, a light guide plate 31 in accordance with a secondpreferred embodiment is similar in principle to the light guide plate21. However, the light guide plate 31 includes two light input surfaces312 at two opposite sides thereof respectively. In this embodiment, thebottom surface 316 defines a center axis X₆ between the two light inputsurfaces 312. Sizes of the dots 318 increase with increasing distance ofthe columns from the first light input surface 312 to the center axisX₆. Sizes of the dots 318 increase with increasing distance of thecolumns from the second light input surface 312 to the center axis X₆. Adistance between two adjacent column axes increases with increasingdistance from the first light input surface 312 to the center axis X₆,and a distance between two adjacent column axes increases withincreasing distance from the second light input surface 312 to thecenter axis X₆. The light guide plate 31 can be assembled with two lightsources (not shown) to form a backlight module. The two light sourcesare disposed adjacent to the two light input surfaces 312 of the lightguide plate 31 respectively. It is to be understood that if the lightsources have different light outputted brightness, any suitable axis(not shown) between the two light input surfaces 312 can be definedinstead of the surface center axis X₆.

Referring to FIG. 4, a light guide plate 41 in accordance with a thirdpreferred embodiment is similar in principle to the light guide plate31. However, a shape of each of dots 418 of the light guide plate 41when viewed from directly below is octagonal.

Referring to FIG. 5, a light guide plate 51 in accordance with a fourthpreferred embodiment is similar in principle to the light guide plate31. However, a shape of each of dots 518 of the light guide plate 51when viewed from directly below is generally heptagonal. It is notedthat in alternative embodiments, the dots 218, 318, 418, 518 of thelight guide plates 21, 31, 41, 51 can have any of various other suitableshapes. For example, when viewed from directly below, the shape can beround, rectangular, or polygonal.

The light source of the present backlight module can be selected fromthe group consisting of at least one light emitting diode and at leastone cold cathode fluorescent lamp. For example, the backlight module mayemploy a plurality of light emitting diodes as the light source.

Finally, while particular embodiments have been described above, thedescription is illustrative of principles of the invention and is not tobe construed as limiting the invention. Various modifications can bemade to the embodiments by those skilled in the art without departingfrom the true spirit and scope of the invention as defined by theappended claims.

1. A light guide plate comprising: a light input surface; a bottomsurface adjacent the light input surface; a top light output surfaceadjacent the light input surface; and a plurality of dots arranged atthe bottom surface in a series of adjacent columns parallel to the lightinput surface, wherein sizes of the dots in a same column progressivelydecrease with increasing distance from a middle of the column to each oftwo opposite ends of the column, sizes of the dots increase withincreasing distance of the columns from the light input surface, eachcolumn defines a column axis that passes through centers of the dots inthat column; and a distance between two adjacent column axes increaseswith increasing distance from the light input surface.
 2. The lightguide plate according to claim 1, wherein an area of the dots whenviewed from directly below is preferably in the range from about 1×10⁻⁷square millimeters to about 1×10⁻⁴ square millimeters.
 3. The lightguide plate according to claim 1, wherein each dot in each column isoffset relative to the adjacent dots in each of the adjacent columns. 4.The light guide plate according to claim 1, wherein a shape of the dotsis selected from the group consisting of round, square, rectangular, andpolygonal.
 5. The light guide plate according to claim 1, wherein amaterial of the dots is one of printing ink, and printing ink matrixmaterial having a plurality of scattering particles uniformly dispersedtherein.
 6. The light guide plate according to claim 1, wherein the dotsare micro-scattering structures etched on the bottom surface.